I once heard a theory on this. The author suggested that time speeds up as one gets older because their world becomes smaller. What I mean by this is, one's experiences grow with time and so there are less new experiences that one utilises. eg...if I am travelling from A to Z for the first time then it appears to take longer due to the anticipation and newness of everything...but if I've travelled that same path over many years the experience appears to be shortened due to the fact that I have done it several times. So time appears to speed up because the older we get, the more experiences we have under our belts...thus time doesn't drag on.